This invention relates to apparatus for closing the guide vanes of a hydraulic machine, more particularly apparatus for stepwisely closing the guide vanes of a water turbine or a pump turbine at different closing speeds.
In the operation of a Francis type water turbine or a pump turbine it is often necessary to interrupt the load or to stop the running at the time of an emergency. In such case, according to prior art closing apparatus, the guide vanes are rapidly closed according to a first stage closing characteristic depicted as 0-1 in FIG. 1 and then closed relatively slowly according to a second stage closing characteristic 1-2 until the guide vanes are completely closed. Such closing characteristic is termed a quickslow two stage closing system. However, in a case where the length of the penstock is long and the flow quantity varies greatly with the number of revolutions as in high head pump turbines, the hydraulic pressure rise caused by water hammer is so great that it is necessary to greatly reduce the closing speed of the guide vanes when the flow quantity is small.
In the case of the two stage closing operation described above, it takes a long closing time at the slow closing stage so that the vanes are subjected to such adverse conditions as vibration, centrifugal force and fluctuation of the hydraulic pressure for a long time before they are returned to the no load opening. Moreover, during normal running as the closing speed of the guide vanes is low its load response characteristic is poor.
To solve this difficulty we have already proposed a method wherein, upon occurence of a load variation, the guide vanes are closed rapidly according to a first stage closing characteristic 0-1 as shown in FIG. 2, slowly closed according to a second stage closing characteristic 1-2 under a running condition in which the flow quantity decreases greatly as the speed of the water turbine increases, and finally closed relatively rapidly according a third closing characteristic 2-3 thereby interrupting the flow of water. (see Japanese patent application No. 16602/1970 which was published as patent publication No. 40902/1974)